Loud speaker



LOUD SPEAKER Filed April 22. 1930 Patented July 18, 1933 PATENT OFFICE FRANSISCUS JOHANNES TEN PAS, OF ALKMAAR, NETHERLANDS LOUD SPEAm Application filed April 22, 1930, Serial No. 446,264, and in Germany February 26, 1930, e

' The invention relates to an improvement in the so-called -inductor dynamic loudspeaker, and has for its object to improve the reproduction,especially ofthe higher frequencies of the frequency range of muslc and speech. a

To this effect according to the invention a modified form offthe armature and/ o1: the

m pole shoes is applied so that a better dlvis on of the magnetic field is obtained.

Up to the present time the motors for loud speakers generally have been made along the line of the disclosure in the patent to C..L.

, Farrand, 1,784,517, of,.December 9th, 1930, wherein the pole shoes in general have been provided; with somewhat narrowed end faces, and in which the armatures carried forwmovement between the respective pole yshoes were so disposed asto have portions thereof extending beyond. the plane .at the edges of the poleslroes. 5 .-.As, is well known, the ideal condition which is desired in motors for. loud speakers is one, in which the flux between the poles at one end of-zthe, armature unit will increase at substantially the same rate that the. flux'between the poles atuthe other end .of the,

armature unit-decreases throughout the 3 stroke, and vice versa, of the armature rod; that is, it .is desired that the total flux at all times will remain a substantially constant quantity.

In motors for loud speakers of the Farrand 3 type, it has been found that due to the narrowness of the pole shoes and the disposition normally of the armatures so that a portion of each thereof extends beyond the plane of the edges of the pole shoes that with the movement of the armature in either direction the number of lines of force emanating from the poles and fiowin through the armature bars changes too suddenly, with the result that the condition wherein the total flux will 46 be constant at all times is not attained.

It is among the objects of this invention to attain this condition by so constructing the pole shoes and assembling and arranging the armatures with respect thereto, whereby wi itherewill be a gradual and linear transition from the largest field intensity between the pole shoes into the field outside of the pole shoes, when the field intensity-approaches and eventually equals zero;

In the drawing an'embodim ent of the invention is illustrated by way of example.

Fig. 1 shows a schematic viewofthe construction of a so-called inductor-dynamic loudspeaker. Y. r

'Fig. 2 isa top view of a pole shoe according to the well-known construction.

Fig. 3 is a schematic front view of.a-construction according to-the zvinvention givenby way ofexample, and

4 illustrates a top view of the pole pieces. s

In the disclosure shown in Figures 1 and 2, N and S representthe north.- and southpoles, each of which has pole shoesE of ,a formation known to the prior art, as, for example, a formation found inthe ,Farrand patent, above specified.

The driving system for thejmot'orcomprises .two ironarmatu-rebars C and .D. rigidly connected by threercross bars'of which only the central bar Mis' shown,of a non-magnetic material-such as brass. The central cross bar M is longerthan the re-' maining cross-bars and actu-ates a conical diaphragm, by means of the aluminum cone K. The usual guide springs (not shown) for controlling the displacement of the driving system in a horizontal direction are provided. Between the armatures and the pole shoes there is a very small air gap, and on one of the legs of each of the north and south poles there is provided a winding, through d which current may pass. Upon the passage of alternating current through both windings the armature between the pole shoes will attain an oscillating movement.

The difiiculty, however, with an arrangement of this type, lies in the fact that normally the armatures as disposed are partially out of the plane defining the edges of the pole shoes so that as current passes through the windings, and there being a small field of greatest magnetic flux insofar as its acts upon the armatures, there will be a tendency 10( as the respective portions of the armatures enter into and pass out of such fields as defined by the planes passing through the edges of the pole shoes, to produce a rapid transition from the largest field intensity between the pole shoes to the zero field intensity outside of the pole shoes, whereby distortion occurs.

The invention tries to remove the said difficulty, as for example to shape the armature bars so that the increase or the decrease of the magnetic flux in the armature bars takes place more gradually in case'the armature moves. To this effect and according to the invention the pole shoes or the armature bars are shaped so that the strength of the field in the armature bars varies in proportion to or substantially in proportion to the horizontal displacement of the armature.

Figs. 3 and 4 show an embodiment of the improvement according to the invention. This embodiment should only be considered as an example.

According to the embodiment as illustrated the end faces 6 of the pole shoes N, S are enlarged outwardly. This enlargement may be provided with a toothed portion g, causing a more equal change in the strength of field in the armature, in case the latter moves. If desired the bars 0 and (1 may be displaced further outwardly than indicated in. Fig. 3.

Of course the embodiment as illustrated is only given by way of example, since the pole shoes may be transformed also in another manner in order to attain the same effect.

Further the teeth 9 or another analogous embodiment may be applied to the armature bars a, d instead of to the pole shoes or to both. In the last case the teeth of the pole shoes may overlap with respect to those of the armature bars.

It appeared experimentall that due to this improvement the repr uction of the hi hest tones was considerably better.

% claim:

1. I11 a. loud speaker of the inductor dynamic type, associated elements comprising of magnet pole shoes and armature bars, at least one of said associated elements having enlarged end face surfaces for the purpose of causing the strength of the magnetic field in the armature bars to vary substantially in direct proportion to the horizontal displacement of the armature bars from normal.

2. In a loud speaker of the inductor dynamic type having cooperating elements comprising of magnet pole shoes and armature bars, the end faces of the magnet pole shoes being enlarged outwardly and provided with projections to cause the strength of the magnetic field in the armature bars to vary in substantially direct proportion to the horizontal displacement of the armature from normal.

3. A loudspeaker motor comprising two pairs of opposite magnetic poles, having their faces enlarged outwardly, each pole being provided with a speech current winding. for increasing the flux through one pair of poles and at the same time diminishing the flux through the other pair of poles, a magnetic field between each pair of magnetic i poles having a homogeneous portion in which the field strength is constant, and a nonhomogeneous portion in which the field strength decreases substantially in direct proportion to the distance to or from the homogeneous portion, an armature consisting of two interconnected soft iron bars, each of said bars being arranged in one of the two non-homogeneous fields, the said bars being narrower than the end faces of the magnetic poles, and said armature being adapted to move in a direction perpendicular to said magnetic poles.

4. A loudspeaker motor, in accordance with claim 3, characterized in that the enlarged portions of the end faces of the poles are provided with projections.

FRANSISCUS JOHANNES TEN PAS. 

